Homozygous babo⁴ mutant larvae display enlarged anal pads.

babo^Np4/babo⁴ mutant larvae display hypotrophy of the central nervous system in late third instar larvae.

Homozygous babo⁴ mutant wing discs are a normal size.

At the the wandering third instar stage, persistent olfactory projection neurons (PPNs) appear to have normal dendritic and axonal projections. These neurons fail to reorganise their processes normally during the first few hours of metamorphosis. However most embryonic-born PPNs still retain dendrites and axons with larval morphology at this time. In the adult mutant fly, severe dendritic and axonal phenotypes are seen in the brain. In a few cases mutant PPNs target an appropriate glomerulus, but also feature ectopic processes. More commonly sparse diffuse processes are seen in the antennal lobe (AL) that are somewhat localised but do not appear to target any specific glomerulus. Processes also occasionally stray to arborize outside the ventral AL. In the most severe cases, sparse dendrites are distributed broadly throughout the AL. In the mushroom body (MB) calyx, all mutant PPN axons appear to retain large larval-like boutons directly on their main trunks (rather tan exclusively terminal swellings on short side branches as in wild-type.) In 64% of cases there are no MB collaterals with wild-type adult appearance. The main trunk is often diverged dramatically from the inner antennocerebral tract in the MB calyx. Finally in the lateral horn (LH), the majority of mutant PPNs feature significant aberrations including unusually profuse swellings along the branches, failure to enter the LH and/or failure to elaborate higher order branches in the LH.

When single cell mutant clones in adult γ neurons, larval projections persist until adulthood in all of these neurons.